Systems and methods for recycling waste plastics, including waste polystyrene

ABSTRACT

Systems and methods for recycling waste plastics are provided, including a system for recovering styrene monomer from waste polystyrene. The system includes a mixing, heating and compacting apparatus to receive a supply of waste polystyrene and to output a densified polystyrene containing melt; a pyrolysis reactor configured to receive the densified polystyrene containing melt and a supply of recycled oligomers, pyrolyze the densified polystyrene containing melt and the recycled oligomers, and output a hydrocarbon gas stream and a solids residue stream; a quenching apparatus configured to receive the hydrocarbon gas stream output from the pyrolysis reactor and condense out oligomers for routing upstream to the pyrolysis reactor to be combined as the supply of recycled oligomers with the densified polystyrene containing melt, and to discharge an altered hydrocarbon gas stream for further processing; and a condenser configured to receive the altered hydrocarbon gas stream from the quenching apparatus and condense out styrene to form a styrene monomer oil product.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.16/388,706, filed Apr. 18, 2019, which is a continuation of U.S. patentapplication Ser. No. 15/436,541, filed Feb. 17, 2017, now U.S. Pat. No.10,301,235, which claims the benefit of U.S. Provisional Application No.62/297,723, filed Feb. 19, 2016, which is incorporated herein byreference in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to the recycling of wasteplastics, including waste polystyrene. Certain embodiments relate morespecifically to systems and methods for pyrolyzing plastic feedstocksand recovering the constituent plastic monomers from which they wereoriginally made, including systems and methods to recover styrene fromwaste polystyrene feedstock.

BRIEF DESCRIPTION OF THE DRAWINGS

The written disclosure herein describes illustrative embodiments thatare non-limiting and non-exhaustive. Reference is made to certain ofsuch illustrative embodiments that are depicted in the figures, inwhich:

FIG. 1 provides a schematic diagram of an embodiment of a plasticrecycling system;

FIG. 2 provides a schematic diagram of another embodiment of a plasticrecycling system; and

FIGS. 3A and 3B provide another schematic diagram of the plasticrecycling system of FIG. 2.

DETAILED DESCRIPTION

Certain embodiments of systems and methods described herein areconfigured for efficient recycling of waste plastics, including wastepolystyrene. Some systems and methods can quickly and simply convertwaste plastics into one or more purified organic molecular species,which can be considered as a crude hydrocarbon material or crude oil.The crude oil may be readily stored, transported, and/or refined intofuel or other commercially relevant materials. In some instances, awaste polystyrene feedstock can be readily converted into a styrenemonomer oil product.

In some embodiments, waste plastic feedstock can be fed continuouslythrough the systems disclosed herein. The feedstock may be pre-meltedvia a mixing, heating and compacting apparatus prior to introductioninto a pyrolysis reactor, which then heats the pre-melted feedstock suchthat the feedstock transitions into a vapor (e.g., one or more gases)for further processing. In some instances, the vapor can be introducedinto a condenser and directly contacted with a pH adjusted solution (orother process solution), which can, in some instances, absorb a portionof the vapor and condense another portion thereof. The condensedmaterial can comprise one or more organic molecular species that can betermed herein as a crude oil. The crude oil can be separated from theother portions of the vapor that are absorbed into the pH adjustedsolution, and thus the crude oil can be of a clean or purified qualitysuch that it may be readily refined from its crude state. In otherinstances, other condensing apparatuses or methodologies may be used tocondense out desirable products from the vapor discharged from thepyrolysis reactor.

In some instances, the feedstock may mainly comprise waste polystyreneand the system may be configured to recover a styrene monomer oilproduct therefrom. In such instances, oligomers may be condensed out ofthe vapor stream discharged from the pyrolysis reactor and may be routedback to the pyrolysis reactor directly or via a vessel designed topre-heat and/or thermally treat the oligomer stream. Additionally, aftercondensing out styrene from the vapor stream, a supplemental condensermay be utilized to condense out light hydrocarbons. The lighthydrocarbons can be stored and/or a portion thereof may be used in aquenching apparatus to assist in condensing out the oligomers forre-introduction through the pyrolysis reactor as described above.

Various illustrative embodiments of inventive systems and methods willnow be described. Advantages of the systems and methods, as well asfeatures and steps thereof, respectively, will be apparent from thedisclosure that follows, including the figures.

FIG. 1 provides a schematic diagram of an embodiment of a plasticrecycling system 10. The plastic recycling system includes a heatingsystem 12 that is configured to deliver heat to a plastic feedstock 14.The heating system 12 can comprise any suitable heating mechanism, suchas, for example, a combustion burner, a fluidized bed burner, a retort,or any other such heating system. In some instances, the heating systemcomprises a pyrolysis recovery unit (PRU). The PRU may include a dualscrew feed mechanism to receive the plastic feedstock and simultaneouslytransport and pyrolyze the feedstock, and to output a hydrocarbon gasstream 16 and a solids residue stream 18. The PRU may include multiplesuccessive zones of heating along a length thereof.

The plastic feedstock 14 can comprise waste plastics of one or morevarieties (e.g., mixed plastics), and may include trace amounts ofnon-plastic contamination or impurities. For example, the impurities maybe of an external nature (e.g., water, foodstuffs, labeling, soil,paper, or cellulose waste) or may result from internal amendments (e.g.,glass, metal, iron, bromine, and/or chlorine). The plastic feedstock 14may be provided in a ground, chipped, or other form that can promote thetransfer of heat thereto. In some instances, the feedstock 14 may bepredominately polystyrene waste.

The plastic feedstock 14 may be fed to the system in a continuousmanner. A feed apparatus can include bins, hoppers, conveyors, mixers,heaters and compactors designed to provide a continuous material feed.The feed apparatus may comprise a mixing, heating and compactingapparatus 20 and may include a compactor and a pre-melter, such as amixer designed to receive the feedstock and output a continuous streamof densified plastic melt. In other instances, the feedstock may be feddirectly into the heating system (e.g. PRU) 12 without being subjectedto pre-melting.

The heat provided by the heating system (e.g., pyrolysis recovery unit)12 can be sufficient to crack or depolymerize the plastic feedstock 14and convert at least a portion thereof into a vapor. The vapor caninclude one or more gaseous organic species, one or more gaseousinorganic species, and/or one or more varieties of entrained particles.In particular, the vapor can include depolymerized non-polar organicgases, which may be desirable for collection and refinement, and whichcan be mixed with impurities. The organic gases can include, forexample, one or more paraffins, olefins, naphthenes, aromatics, and/orother classes of hydrocarbon materials. The mixed-in impurities caninclude, for example, inorganic acids (e.g., hydrochloric acid,hydrobromic acid), entrained metals or metalloids (e.g., cadmium, iron,antimony); and/or organic acids (e.g., terephthalic acid). In someembodiments, the vapor may include additional molecular species, such aspolar organic molecules, which may or may not be collected with thenon-polar organic molecules. For example, the vapor can include one ormore alcohols, ketones, ethers, phenols, carboxylic acids, or otherpolar organic molecules.

In some embodiments, the plastic feedstock may be heated under vacuumconditions, or under negative pressure. In other embodiments, theplastic feedstock may be heated under positive pressure. In still otheror further embodiments, the plastic feedstock may be heated underatmospheric pressure conditions, or under any suitable combination ofthe foregoing (e.g., the pressure may be varied during a heating event).

The vapor can be delivered to a vapor treatment system 22 that effects aphase change of at least a portion of the vapor such that certainmolecules transition from a gaseous state to a liquid state. The vaportreatment system 22 may also be referred to as a vapor treatment unit ora vapor treatment vessel. The vapor treatment system 22 may include a pHadjusted solution (or other process solution) that is used to effect thecondensation. Moreover, the pH adjusted solution can be configured toabsorb at least a portion of the impurities from the vapor. Embodimentsof the solution can readily absorb organic acids, inorganic acids,metals, metalloids, and/or certain polar organic molecules. The term “pHadjusted solution” is used in a broad sense and includes solutions thatare not pH neutral and that exhibit any or all of the various propertiesdescribed herein. For example, a pH adjusted solution can be formulatedto remove impurities from the vapor, and in further embodiments, can beimmiscible with condensed oils so as to be readily separated therefrom.For example, in some embodiments, the pH adjusted solution can comprisean acidic solution, which may, in some cases, be strongly acidic. Infurther embodiments, the pH adjusted solution can comprise a bufferedaqueous solution adjusted to a desired pH value. In various embodiment,the pH adjusted solution can have a pH value that is less than 7, lessthan about 6.5, less than about 6, less than about 5.5, less than about5, less than about 4, or less than about 3.

The pH adjusted solution can include one or more chemical amendments ofany suitable variety to achieve the desired properties of the solution.Such properties can include, for example, the ability to remove one ormore impurities from the vapor and/or a high immiscibility with oil.Adjustment or optimization of one or more of foregoing properties may beachieved by altering the concentration of the one or more chemicalamendments within the pH adjusted solution. For example, the presence,combination, and/or concentration of one or more materials within the pHadjusted solution can optimize removal of contaminants from the vapor asit interacts with the pH adjusted solution. In various embodiments, thepH adjusted solution can include strong and/or weak inorganic acids(e.g., hydrochloric acid, acetic acid), one or more pH buffer solutions(e.g., acetic acid+sodium acetate), one or more chelating agents (e.g.,ethylenediaminetetraacetic acid (EDTA)), and/or one or more coagulantsand/or flocculants (e.g., calcium hydroxide, polyacrylamide).

The vapor treatment system 22 can be configured to effect direct contactbetween the vapor received therein and the pH adjusted solution (orother process solution). For example, as further discussed below, insome embodiments, the pH adjusted solution may be sprayed into contactwith the vapor, whereas in other embodiments, the vapor may be bubbledthrough the solution. The pH adjusted solution can absorb or dissolveportions of the vapor (e.g., organic acids, inorganic acids, metals,metalloids, and/or certain polar organic molecules). The pH adjustedsolution also can be provided at a lower temperature than that of thevapor such that the solution condenses at least those portions of thevapor that are immiscible therein (e.g., non-polar organic molecules).

Those portions of the condensed vapor that are immiscible in the pHadjusted solution (i.e., the hydrophobic portions) can be readilyseparated from the solution. In some embodiments, the separation (or atleast one or more stages thereof) takes place within the vapor treatmentsystem, whereas in other embodiments, the separation (or at least one ormore stages thereof) takes place within a separator 24 that isindependent of the vapor treatment system 22.

In some embodiments, the immiscible portions are removed from the vaportreatment system as a form of crude oil 26. The crude oil 26 thus canhave few or no impurities, as the impurities that were present in theplastic feedstock are dissolved or absorbed into the pH adjustedsolution. In some embodiments, at least some of the dissolved orabsorbed impurities can remain within the pH adjusted solution withinthe vapor treatment system 22. For example, in some instances, after thepH adjusted solution has amassed the impurities, it may continue to beused within the vapor treatment system 22, such that the impurities arenot removed (at least not immediately) from the vapor treatment system.In other or further embodiments, dissolved or absorbed impurities areremoved from the vapor treatment system 22 separately from the oil.

Certain classes of polar organic molecules may only partially (or atleast partially) partition into the pH adjusted solution. For example, aportion of certain alcohols, ketones, ethers, phenols, carboxylic acids,and/or other polar organic molecules may partition into the pH adjustedsolution and another portion thereof may partition into the crude oil.Accordingly, in some embodiments, crude oil that includes a portion of aspecies of polar organic molecules may be separated from a pH adjustedsolution that contains another portion of the species of polar organicmolecules.

The vapor may include portions that do not condense within the vaportreatment system 22 and are not absorbed by the pH adjusted solution.Such non-condensable gases 29 can be removed separately from the vaportreatment system 22, and may be combusted or disposed of in any othersuitable manner.

In various embodiments, the vapor treatment system 22 may operate undervacuum conditions, or under negative pressure. In other embodiments, thevapor treatment 22 system may operate under positive pressure. In stillother or further embodiments, the vapor treatment system 22 may operateunder atmospheric pressure conditions, or under any suitable combinationof the foregoing (e.g., the pressure may be varied during a condensingevent).

The system can be well suited for quickly cracking or depolymerizing theplastic feedstock. For example, in some embodiments, heating of theplastic feedstock and conversion thereof into the vapor can be performedat high temperatures at which a variety of different molecular speciesmay be gasified simultaneously. Such different molecular species mighthave different vaporization temperatures at a given pressure, and atemperature at which the plastic feedstock is heated can exceed thistemperature for some or all of the molecular species. The molecularspecies can then be separated from each other when the vapor isdelivered to the vapor treatment system, as previously described.Accordingly, the system can operate without the heating system slowlyheating up and occasionally holding steady at various discreettemperature levels along the way so as to allow for individual molecularspecies to be gasified sequentially. It is to be appreciated, however,the system may also be used in an operational mode in which the heatingsystem and the plastic feedstock progress through a series of sequentialheating steps or levels, as just described.

The system 10 can include a vacuum system 30 that is configured tomaintain a negative pressure within the heating system (e.g., PRU) 12and within the vapor treatment system 22. The vacuum system 30 cancontinuously evacuate gases from the heating system (e.g., PRU) 12 suchthat depolymerization of the plastic feedstock occurs in anoxygen-deprived or oxygen-free environment. The vacuum system 30 drawsthe vapor into the vapor treatment system 22, where it is contacted bythe pH adjusted solution, or non-PH adjusted solution, or otherwiseprocessed by a condensing apparatus or device. The vacuum system 30draws the non-condensable gases from the vapor treatment system 22, andmay distribute them to a combustion unit or other suitable disposaldevice 32.

The system 10 may include a coalescer/separator 24 that receives anemulsion of condensed material from the vapor treatment system 22. Theemulsion can comprise crude oil that includes a small amount of the pHadjusted solution (or other process solution) entrained therein. Thecoalescer/separator 24 can be configured to separate the crude oil 26from the pH adjusted solution (or other process solution) based on thedifference in relative density between these materials. For example, thecoalescer/separator 24 can comprise a settling tank that allowsgravitational separation of the solution from the crude oil 26. In otherembodiments, the coalescer/separator 24 may comprise a centrifuge orother separator device.

The system 10 can further include a variety of sensor and controlcomponents (not shown). For example, the system 10 can include one ormore pressure sensors and/or temperature sensors, which can provide to acontroller various data regarding the operation of the heating system(e.g., PRU) 12 and the amount of heat being delivered to the feedstock.The sensors can communicate with a controller in any suitable manner,such as by wired or wireless connection. The controller can alteroperational parameters of the heating system (e.g., PRU) 12 in responseto data received from the sensors and/or as a result of otherprogramming.

A master control system may be configured to communicate with thecontroller, and may also be configured to communicate with additionalcontrollers that may each be dedicated to subsystems of the plasticrecycling system. For example, separate subsystem controllers may bededicated to the vapor treatment system 22 and the vacuum system 30,respectively. In some embodiments, subsystem controllers may be situatedlocally (e.g., near the various subsystems with which they areassociated), whereas the master control system may be situated in asupervisory station in which an operator can monitor the instantaneousstatus of the subsystems of the system 10 and make changes thereto asdesired, whether onsite or offsite.

For the sake of convenience, subsystem controller(s) associated with aparticular component may not be identified hereafter, nor will it beexplicitly stated that a particular subsystem controller and/or themaster control system is able to monitor and/or control the operation ofa particular component of the plastic recycling system 10, although suchis understood. It is also noted that steps or control events discussedherein which can be effected by sub-controllers and/or the mastercontrol system may be embodied in machine-executable instructions thatare to be executed by a general-purpose or special-purpose computer (orother electronic device). Alternatively, the steps or control events maybe performed or instigated by hardware components that include specificlogic for performing the steps or control events, or by a combination ofhardware, software, and/or firmware. Some or all of the steps may beperformed locally (e.g., via a subsystem controller) or remotely.

As the feedstock is heated in the heating system (e.g., PRU) 12, theplastic feedstock eventually gasifies or vaporizes. The vapor can beintroduced into the vapor treatment system 22 in any suitable manner.For example, in some embodiments, the vapor may be introduced into acondensing tower of a condenser substantially without altering atrajectory of the vapor. In other embodiments, the vapor may encounter abaffle upon entering the condensing tower.

Those portions of the vapor that are not condensed (i.e.,non-condensable gases) may be passed to a caustic scrubber, which passesthe remaining vapor through a caustic solution so as to chemically scrubthe vapor (e.g., remove mercaptan sulfur species therefrom) and so as toneutralize trace levels of free inorganic acids. The remainder of thevapor may pass from the caustic scrubber through to an emissions controldevice (ECD) 32. Any suitable vacuum system 30 may be used with theplastic recycling system 10 to move the vapor accordingly.

Any suitable emissions control device (ECD) 32 can be used with theplastic recycling system 10. In some embodiments, the emissions controldevice 32 can comprise a burner or other combustion device. Exhaust 34from the emissions control device 32 may be vented to atmosphere. Inother embodiments, the hot exhaust 34 may instead be transferred toother portions of the plastic recycling system 10.

The absorbed and condensed portions of the vapor may settle into a tankof the coalescer/separator 24 that includes one or more weirs. The pHadjusted solution (or other process solution), which retains theabsorbed impurities, may facilitate coagulation of some contaminantswhich have a greater relative density than the condensed crude oilmaterial 26, and may settle to the bottom of the tank. Accordingly, thecondensed crude oil 26 rises to the top of the tank and flows over theone or more weirs to be collected for further processing 36, storage 38or use.

In addition, downstream processing may be provided in some embodimentsto purify the product streams discussed herein or fractionate saidstreams into specified hydrocarbon cuts. Process units for this purposemay include, but are not limited to, distillation, solvent extraction,adsorption, and catalyst treatment units.

In some instances, one or more supplemental condensers 40 may beprovided to condense out light hydrocarbons 42 from the quenchedpyrolysis gas 28. The one or more streams of light hydrocarbons 42 maythen be combined with the crude oil product 26, or may be stored asseparate hydrocarbon products.

FIG. 2 and FIGS. 3A and 3B provide schematic diagrams of anotherembodiment of a plastic recycling system 100, which is particularly wellsuited for producing a styrene monomer oil product 126 from wastepolystyrene 114. Similar to the aforementioned system, a mixing, heatingand compacting apparatus (e.g., a mixer) 120 may be provided to receivea supply of waste polystyrene 114 and to output a densified polystyrenecontaining melt 121. The system 100 may further include a pyrolysisrecovery unit (PRU) 112 that is configured to receive the densifiedpolystyrene containing melt 121 and pyrolyze the densified polystyrenecontaining melt 121 and output a hydrocarbon gas stream 116 and a solidsresidue stream 118. The PRU 112 may comprise, for example, a dual screwfeed mechanism within a reactor shell which is configured tosimultaneously transport and heat the feedstock introduced into the PRU112. The PRU 112 may have multiple zones of heating along a lengththereof to effectively heat the feedstock to a pyrolysis temperature asthe material progresses from one end of the PRU 112 to the other.

The system 100 may further comprise a quenching apparatus 122 that isconfigured to receive the hydrocarbon gas stream 116 output from the PRU112 and to condense out oligomers (e.g., dimers and trimers) 123 forrouting upstream to the PRU 112. In this manner, a portion of thefeedstock can be continuously refined to provide an exceptionallypurified styrene monomer oil product. The quenching apparatus 122 mayalso be configured to discharge an altered hydrocarbon gas stream 128for further processing. A condenser 140 may be provided to receive thealtered hydrocarbon gas stream 128 from the quenching apparatus 122 andto condense out styrene to form the styrene monomer oil product 126.Additionally, a supplemental condenser 141 may be provided to receive adischarged gas stream from the styrene condenser 140 and to condense outlight hydrocarbons 142 which may form a light hydrocarbon product or maybe combined with other streams. The supplemental condenser 141 may beconfigured to direct a portion of the light hydrocarbons 142 upstream tothe quenching apparatus 122 to assist in condensing out the oligomers123 from the hydrocarbon gas stream 116 output from the PRU 112. Anyremaining non-condensable gasses 129 may be processed as described inconnection with the aforementioned system, including processing by anappropriate emissions control device 132 and under the influence of avacuum system 130.

In addition, downstream processing may be provided in some embodimentsto purify the product streams discussed herein or fractionate saidstreams into specified hydrocarbon cuts. Process units for this purposemay include, but are not limited to, distillation, solvent extraction,adsorption, and catalyst treatment units.

FIGS. 3A and 3B provide a schematic flow diagram of aspects andfunctionalities of system 100 with representative temperature data. Theschematic flow diagram includes various industry standardized piping andinstrument diagram symbols and abbreviations, including, for example,the abbreviations AMB, PC, CWS, TC, CWR, CHS, CHR, ECD, LC, and SC,wherein: AMB means ambient temperature; PC means pressure controller;CWS means cooling water supply; TC means temperature controller; CWRmeans cooling water return; CHS means chilled water supply; CHR meanschilled water return; ECD means emissions control device; LC means levelcontroller; and SC means speed controller.

Additional components, features and functionality of the systems will bereadily apparent to those of ordinary skill in the relevant art upon areview of the detailed schematic diagrams provided in the Figures.

Moreover, it will be understood by those having ordinary skill in therelevant art that changes may be made to the details of the embodimentsdescribed and illustrated herein without departing from the underlyingprinciples presented herein. For example, any suitable combination ofvarious embodiments, or the features thereof, is contemplated. Forexample, various embodiments may be configured to operate in one or moreof a batch mode, a continuous batch mode, or a continuous mode. Other orfurther embodiments may include a condenser system and/or othercomponents that are configured to operate under one or more of vacuumconditions, atmospheric pressure conditions, or positive pressureconditions.

Any methods disclosed herein comprise one or more steps or actions forperforming the described method. The method steps and/or actions may beinterchanged with one another. In other words, unless a specific orderof steps or actions is required for proper operation of the embodiment,the order and/or use of specific steps and/or actions may be modified.

Throughout this specification, any reference to “one embodiment,” “anembodiment,” or “the embodiment” means that a particular feature,structure, or characteristic described in connection with thatembodiment is included in at least one embodiment. Thus, the quotedphrases, or variations thereof, as recited throughout this specificationare not necessarily all referring to the same embodiment.

Similarly, it should be appreciated that in the above description ofembodiments, various features are sometimes grouped together in a singleembodiment, figure, or description thereof for the purpose ofstreamlining the disclosure. This method of disclosure, however, is notto be interpreted as reflecting an intention that any claim require morefeatures than those expressly recited in that claim. Rather, inventiveaspects lie in a combination of fewer than all features of any singleforegoing disclosed embodiment. It will be apparent to those havingskill in the art that changes may be made to the details of theabove-described embodiments without departing from the underlyingprinciples set forth herein.

The invention claimed is:
 1. A method of recovering a monomer from wastepolymer, the method comprising: mixing, heating and compacting a supplyof waste polymer to form a densified polymer containing melt; supplyingthe densified polymer containing melt to a pyrolysis reactor along witha supply of recycled oligomers; pyrolyzing the densified polymercontaining melt and recycled oligomers within the pyrolysis reactor togenerate a hydrocarbon gas stream and a solids residue stream;condensing out oligomers from the hydrocarbon gas stream output from thepyrolysis reactor with a quenching apparatus and routing the oligomersupstream to the pyrolysis reactor to be combined as the supply ofrecycled oligomers with the densified polymer containing melt;discharging an altered hydrocarbon gas stream from the quenchingapparatus; condensing out a monomer from the altered hydrocarbon gasstream with a primary condenser to form a monomer oil product and adischarged gas stream; condensing out a hydrocarbon fraction from thedischarged gas stream with a secondary condenser; and directing a streamof hydrocarbons from the hydrocarbon fraction output from the secondarycondenser upstream to the quenching apparatus to assist in condensingout the oligomers from the hydrocarbon gas stream output from thepyrolysis reactor.
 2. The method of claim 1, wherein the densifiedpolymer containing melt is supplied to the pyrolysis reactor in acontinuous manner.
 3. The method of claim 1, wherein pyrolyzing thedensified polymer containing melt and recycled oligomers within thepyrolysis reactor includes simultaneously transporting and heating thedensified polymer containing melt and recycled oligomers with a dualscrew feed mechanism.
 4. The method of claim 1, wherein the supply ofwaste polymer is predominately polystyrene waste and the monomer isstyrene.
 5. A method of recovering a monomer from waste polymer, themethod comprising: pyrolyzing a polymer feedstock and a supply ofrecycled oligomers within a pyrolysis reactor to generate a hydrocarbongas stream and a solids residue stream; condensing out oligomers fromthe hydrocarbon gas stream output from the pyrolysis reactor with aquenching apparatus and routing the oligomers upstream to the pyrolysisreactor to be combined as the supply of recycled oligomers with thepolymer feedstock; discharging an altered hydrocarbon gas stream fromthe quenching apparatus; condensing out a monomer from the alteredhydrocarbon gas stream with a primary condenser to form a monomer oilproduct and a discharged gas stream; condensing out a hydrocarbonfraction from the discharged gas stream with a secondary condenser; anddirecting a stream of hydrocarbons from the hydrocarbon fraction outputfrom the secondary condenser upstream to the quenching apparatus toassist in condensing out the oligomers from the hydrocarbon gas streamoutput from the pyrolysis reactor.
 6. The method of claim 5, furthercomprising: mixing, heating and compacting a supply of waste polymer toform the polymer feedstock; and supplying the polymer feedstock to thepyrolysis reactor along with the supply of recycled oligomers.
 7. Themethod of claim 5, wherein the polymer feedstock is supplied to thepyrolysis reactor in a continuous manner.
 8. The method of claim 5,wherein pyrolyzing the polymer feedstock and the supply of recycledoligomers within the pyrolysis reactor includes simultaneouslytransporting and heating the polymer feedstock and the supply ofrecycled oligomers with a dual screw feed mechanism.
 9. The method ofclaim 5, wherein the waste polymer is predominately polystyrene wasteand the monomer is styrene.